The Neural Engine is a completely separate hardware block, and you have good reasons to have such an extension available on the CPU directly, to reduce latency for short-running tasks.
Is it possible AMX is implemented with the implementation-defined system registers and aliases of SYS/SYSL in the encoding space reserved for implementation-defined system instructions? Do you have the encodings for the AMX instructions?
A sample instruction: 20 12 20 00... which doesn't in any stretch parse as a valid arm64 instruction in the Arm specification.
Edit: Some other AMX combinations off-hand:
00 10 20 00
21 12 20 00
20 12 20 00
40 10 20 00
Let me repeat this: part of the ARM architectural license says that you can't modify the ISA. You have to implement a whole subset (the manual says what's mandatory and what's optional), and only that. This is, as I've been saying, public knowledge. This is how it works. And there are very good reasons for this, like avoiding fragmentation and losing control of their own ISA.
And once again, stop spreading misinformation.
Specifically about the Apple case,
After your tone, not certainly obligated to answer but will write one quickly...
Apple A13 adds AMX, a set of (mostly) AI acceleration instructions that are also useful for matrix math in general. The AMX configuration happens at the level of the AMX_CONFIG_EL1/EL12/EL2/EL21 registers, with AMX_STATE_T_EL1 and AMX_CONTEXT_EL1 being also present.
The list of instructions is at https://pastebin.ubuntu.com/p/xZmmVF7tS8/ (didn't bother to document it publicly at least at this point).
Hopefully that clears things up a bit,
And please don't ever do this again, thank you. (this also doesn't comply with the guidelines)
-- a member of the checkra1n team